1. Field of the Invention
The present invention relates to a light emitting semiconductor device which is constituted using semiconductor layers.
2. Description of the Prior Art
Heretofore there has been proposed a light emitting semiconductor device of the type that p and n type single crystal semiconductor layers are formed one on the other to define therebetween a pn junction. In this case, the single crystal semiconductor layers are usually formed of direct gap semiconductors of the III-V compounds, such as GaAs, GaAs.sub.1-x P(0&lt;x&lt;1),Ga.sub.1-x Al.sub.x As(0&lt;x&lt;1) and so forth. The reason for using such direct gap III-V compound semiconductors is that they provide for enhanced light emission efficiency as compared with indirect gap III-V compound semiconductors. However, the formation of such semiconductor layers involves much difficulty as the semiconductor constituting the layers must be provided in a single crystal form.
Accordingly, the conventional light emitting semiconductor device using semiconductor layers of the direct gap III-V compound semiconductors are difficult and expensive to manufacture.
Furthermore, in the prior art light emitting semiconductor device it is customary that the two single-crystal semiconductor layers laminated to define therebetween the pn junction are formed of direct gap single-crystal III-V compound semiconductors of the same composition, i.e. of the same energy gap, and hence the pn junction is a homojunction.
With such a light emitting semiconductor device, when applying a forward bias voltage to the pn junction so as to emit light, the barrier height of the pn junction is decreased, facilitating electrons from the n type semiconductor layer to diffuse deeply into the p type semiconductor layer across the pn junction and holes from the p type semiconductor layer to diffuse deeply into the n type semiconductor layer across the pn junction.
This leads to the shortcoming of impaired light emission efficiency.